Electroluminescent display device with selected indicia



Nov. 23, 1965 v. voDlcKA 3,219,865

ELECTROLUMINESCENT DISPLAY DEVICE WITH SELECTED INDICIA Filed May l, 1963 2 Sheets-Sheet 1 ../lll/l yl//l//xXl/l v\\\ \\L\ \l\\\\\|`\ mmmmwmw memwwmwmwmmmw Nov. 23, 1965 v. VODICKA 3,219,865

ELEGTROLUMINESCENT DISPLAY DEVICE WITH SELECTED INDICIA Filed May l, 1963 2 Sheets-Sheet 2 InverwrlQT-z Vincencc Vodicka United States APatent O 3,219,865 ELECTROLUMINESCENT DISPLAY DEVICE WITH SELECTED INDICIA Vincent Vodicka, South Euclid, Ohio, assignor to General Electric Company, a corporation of New York Filed May 1, 1963. Ser. No. 277,305

9 Claims. (Cl. 313-108) v This invention relates in general to electroluminescent cells or lamps and more particularly, to an electroluminescent cell or lamp in the form of an electroluminescent display device or panel such as a digital display or readout device and to a method of making such a device.

Electroluminescent cells or llamps in the form of display devices or panels such as digital display or read-out devices are well known in themselves at present as disclosed, for example, in U.S. Patent 2,922,993, E. A. Sack, Ir. Such devices comprise in general a layer of a suitable electroluminescent phosphor sandwiched between a pair of electrically conductive layers one of which is light-transmitting and the other of which is subdivided into a plurality of discrete electrode sections of predetermined shape and array such that, upon selective application of an A.C. potential across the light-transmitting electrode layer and one or more of the discrete electrode sections, the areas of the phosphor llayer overlying the discrete electrode sections selectively energized are caused to luminesce, thereby producing the desired luminous pattern from the device such as, for example, a digit or a letter.

While the current supply leads to the individual electrode sections of such electroluminescent display devices or panels may be terminated through the back or nonviewing side of the display panel, it is preferable that they be terminated at the peripheral edges or rim of the panel, since with such a method of termination the display panel can be desirably kept to a minimum thickness and also free of projecting contact terminals at the back side. However, the necessity for keeping the individual leads to the various electrode sections of such edge contact terminated type electroluminescent display panels from crossing and so electrical-ly contacting any of the other leads or electrode sections of the panel has resulted, in prior type edge contact terminated electroluminescent display panels as heretofore generally constructed, not only in a loss of available display area for a given panel surface area, but also in a loss in definition of the illuminated display patern owing to the necessity for spacing certain ones of the electrode sections sufficiently far apart to permit passage therebetween of a lead without touching and electrically contacting such electrodes. Moreover, the design and manufacture of such edge contact terminated type electroluminescent display panels heretofore has been complicated by the necessity for incorporating therein some provision for preventing the leads themselves, as well as the electrode sections to which they are connected, from capacitively coupling to the light-transmitting electrode upon application of A.C. ptential thereacross, with resulting undesired light emission from the portions of the phosphor layer directly overlying the energized lead or leads such as would normally detract from the appearance of the illuminated display pattern.

It is an object of the invention, therefore, to provide a novel form of electroluminescent display device or panel of the edge contact terminated type which permits maximum utilization of the available surface area thereof for display electrode purposes and affords improved definition of the illuminated display pattern or patterns produced by the device.

Another object of the invention is to provide an elecice troluminescent display device or panel of the edge contact terminated type having a simplified structural arrangement, easily incorporable into the device during manufacture, for preventing the current supply leads to the discrete electrode sections of the device from capacitively coupling to the light-transmitting electrode thereof during operation.

A further object of the invention is to provide a novel method of making an electroluminescent display device or panel if the edge contact terminated type.

Briefly stated, in accordance with one aspect of the invention, the current supply leads which are electrically connected to respective ones of the segmented electrode sections of an electroluminescent display device of the edge contact terminated type are electrically insulated from the phosphor layer, yand from the electrode sections other than at the regions of their respective electrical connection thereto, by an intervening preformed insulator sheet of an organic thermoplastic material of low dielectric constant or permittivity having apertures underlying respective ones of the electrode sections, through which apertures the electrode sections are contacted by and electrically connected with respective ones of the current supply leads. Because of its low permittivity, the insulator sheet also serves to effectively prevent the portions of an energized current supply lead, other than those portions which are shielded by an overlying energized electrode section, from capacitively coupling to the light-transmitting electrode of the device and so causing undesired luminescence of the portions of the phosphor layer overlying such Unshielded lead portions.

In accordance with a further aspect of the invention, the back or pattern-forming electrode component of an electroluminescent display device or panel is constituted by a composite two-layer laminate or base electrode assembly comprised of a base sheet of a plastic film provided with printed or otherwise suitably deposited circuit leads for the various discrete back electrode sections of the device, and an overlying preformed insulator sheet of a plastic lilm of low dielectric constant organic thermoplastic material laminated at one side to the printed circuit side of the base sheet and having the discrete back electrode sections printed or otherwise suitably deposited on its other side so as to contact and make electrical connection with the respective circuit leads through registered apertures in the insulator sheet. The base electrode assembly or prelaminate thus formed is then assembled togetber with an electroluminescent phosphor layer and an overlying light-transmitting front electrode layer, as by laminating it thereto, to thereby form the completed electroluminescent display device or panel according to the invention.

Further objects and advantages of the invention will app-ear from the following detailed description of species thereof and from the accompanying drawing.

In the drawing, FIG. l is an exploded perspective view illustrating one of the initial steps in the manufacture of an electroluminescent display device according to the invention wherein an apertured plastic insulator sheet is assembled together with a plastic base sheet to overlie electrical circuit leads deposited thereon.

FIG. 2 is a plan view of the assembled insulator sheet and circuit-carrying sheet components shown in FIG. l, with terminal contacts attached thereto.

FIG. 3 is a plan view illustrating a subsequent step in the manufacture of the electroluminescent display device according to the invention wherein the discrete back electrode sections thereof are coated or printed onto the apertured insulator sheet of the base circuit assembly shown in FIG. 2 so as to electrically connect with respective ones of the circuit leads thereof through registering apertures in the insulator sheet.

FIG. 4 is a sectional view of the electrode base assembly shown in FIG. 3, on the line 4-4 thereof.

FIG. 5 is a fragmentary sectional View of one form of electroluminescent display device according to the invention.

FIG. 6 is a sectional view of the lay-up assembly of component elements for making an encapsulated type of electroluminescent display advice according to one method comprising my invention.

FIG. 7 is a similar sectional View of the lay-up assembly of component elements for making an encapsulated type of electroluminescent display device by another method according to the invention.

FIG. 8 is a perspective view of a modified form of base circuit assembly for making a modified electroluminescent display device according to the invention.

FIG. 9 is a plan view of a modified form of composite electrode base assembly formed by applying a segmented back electrode layer onto the modified base circuit assembly of FIG. 8.

FIG. 10 is a plan view of a composite front electrode and moisture barrier assembly for use in fabricating the modified form of electroluminescent display device acc-ording to the invention employing the composite electrode base assembly shown in FIG. 9.

FIG. 11 is a fragmentary sectional view of the lay-up assembly of composite elements for making such -a modified form of electroluminescent display device according to the invention.

FIG. 12 is a fragmentary sectional View of another modified form of electroluminescent display device according to the invention having an outer plastic stiifening layer afixed thereto, and

FIG. 13 is a perspective view of a completed electroluminescent display device -according to the invention embodying the modified structure shown in FIG. 12.

Referring to the drawing, the invention is therein illustrated, for purposes of representation, as appiled to an electroluminescent display panel in the form of a digital display device or read-out lamp 1 adapted to selectively display, in a luminous pattern, any digit or numeral from 0 to 9, as desired. It should be understood, however, that the invention is applicable as well to various other forms of electroluminescent display devices for the selective display of various other types or forms of indicia, characters, patterns or designs.

As shown in FIG. 5, the electroluminescent display devise 1 according to the invention is comprised in general of an electrically active assembly comprising a thin electrolum-inescent phosphor layer 2, and preferably in add-ition a thin contiguous insulating layer 3 of high dielectric constant material, sandwiched between a light-transmitting electrically conductive front electrode layer 4 and a segmented back electrode layer 5 which is disposed next to the insulating layer 3, Where such is employed. The phosphor layer 2 is constituted by a self-supporting sheet or film comprising a conventional type electroluminescent phosphor such as, for example, Zinc sulfide-zinc oxide combined with suitable activators such as copper, manganese, lead, or silver, dispersed in a suitable organic polymeric matrix material of high dielectric constant material such as is commonly employed for such purpose in socalled organic type electroluminescent cells or lamps, as disclosed for example in U.S. Patent 2,945,976, Fridrich et al., dated July 19, 1960. As therein indicated, Ihowever, plasticized cyanoethyl polyglucosides such as cyanoethyl cellulose plasticized with cyanoethyl phthalate, as described and claimed in copending application Serial No. 701,907, Jaffe, filed December 10, 1957, and U.S. Patent 2,951,865, Jaffe et al., dated September 6, 1960, both assigned to the same assignee as the present invention, are preferred organic matrix materials which form a dense tough film of high dielectric constant and good mechanical and thermal stability. The insulating layer 3 1s comprised of a finely divided insulating material of high dielectric constant such as, for example, barium titanate or titanium dioxide, dispersed in a suitable high dielectric constant organic polymeric matrix material such -as that employed for the phosphor layer 2, preferably `cyanoethyl cellulose plasticized lwith cyanoethyl phthalate as `referred to above. The light-transmitting electrically conductive front electrode layer 4 may be any type conventionally employed for such purpose in electroluminescent cells or lamps such as, for example, electrically conductive glass paper as disclosed in U.S. Patent 2,849,339, Jaffe, dated August 26, 1958, and comprising commercially available micro-fiber .glass paper around 0.001 inch thick which has been rendered electrically conductive in any suitable manner, as by dipping the paper in a solution of a suitable metal salt such as indium basic triuoroacetate and subsequently drying and baking the paper at elevated temperatures to provide a conductive coating on the surface portion of the constituent glass fibers. Preferably, however, the electrode layer 4 is comprised of a light-transmitting electrically conductive lacquer such as, for example, that described and claimed in copending U.S. application Serial No. 189,095, Jaffe et al., filed April 20, 1962, and assigned to the assignee of the present invention, and comprising a dispersion of electrically conductive light-transmitting particulate material, such as indium oxide or crushed electrically conductive glass paper as described hereinabove, in a light-transmitting organic plastic matrix material such as, for example, that employed as the matrix material for the phosphor and insulating layers 2 and 3.

As shown in FIGS. 3 and 4, the segmented back electrode layer 5 is formed in accordance with the invention as a part of a composite electrode base assembly 6 and comprises an array of discrete electrically conductive electrode sections or areas which correspond in shape and array to the particular pattern of illumination desired when an A.C. potential is applied across the front electrode 4 and one or more of the back electrode sections. In the case of the particular digital display or read-out device illustrated, the segmented electrode 5 is composed of seven bar-shaped principal electrode sections or areas 7 to 1-3 arranged in -two side-by-side substantially square or parallelogram shaped patterns having a common side so as to delineate the block number 8 located more or less centrally within and longitudinally aligned with the rectangularly shaped display area of the device. As shown, the electrode sections 7 to 13 are spaced apart a slight distance at the points where they meet, for example, a distance of around 1 mil, so as to be electrically insulated from each other. By applying an A.C. potential across the front electrode 4 and preselected ones of the back electrode sections 7 to 13, in the manner such as disclosed for example in the aforementioned U.S. Patent 2,922,993, any digit from 0 to 9 may be made to light up on the display panel. Preferably in addition, the composite back electrode layer 5 is also comprised of one or more (three in the case of the particular digital display device illustrated) discrete electrode sections 14 conforming to the background of the display panel enclosed by and surrounding the composite figure 8 formed by the bar-shaped principal electrode sections '7 to 113. By the provision of these additional background electrode sections -14, it is possible for the display device 1 to selectively display the desired digit or other indicia either as a lighted configuration against a darkened background, or as darkened configuration against a lighted background. 'Ihe background electrode sections 14 are, of course, spaced a slight distance at their marginal edges from the adjacent bar-shaped principal electrode sections 7 to 13 so as to be electrically insulated therefrom.

Referring to FIGS. 1 to 4, the composite electrode base assembly 6 is formed by laminating together two sheets 15 and 16 of fiexible organic thermoplastic film one of which, e.g., the base sheet 15, carries the electrical circuitry or electrically conductive leads 7a to 14a for the various electrode sections 7 to 14 which are applied to the top or insulator sheet 16 after the lamination thereof to the base sheet 15. The plastic base sheet may be made of any durable thermoplastic organic resin or polymeric film material. Preferably, however, it is made of a plastic material which exhibits hydrophilic properties, i.e., has an .affinity of water. Examples of suitable plastic sheet materials have such hydrophilic properties are nylon 6, 6, and nylon 6 such as that commercially known as Caplene. For the purposes of the invention, the plastic insulator sheet 16 is formed of a suitable organic thermoplastic material having a low dielectric constant or permittivity. Examples of organic thermoplastic materials of low permitivity which may be suitably employed for the plastic insulator sheet 16 are polytetraluoroethylene, polyethylene, polychlorotrifluoroethylene, and nylons such as the nylon 6 and nylon 6, 6 material mentioned above.

In fabricating the composite electrode base assembly 6 according to the invention, the electrically conductive current supply or circuit leads 7a to 14a for the respective electrode sections 7 to 14 of the segmented back electrode layer 5 are first suitably applied to one side of the plastic base sheet 15 which, for the purposes of the invention, may have a thickness around 2 to 6 mils or so, with .a thickness around 6 mils being preferred. The circuit leads 7a to 14a are preferably applied to the plastic base sheet 15 in the form of a printed circuit comprised of stripe-shaped coatings of suitable electrically conductive material which are deposited on the plastic sheet by any suitable process, as by a silk screen printing process, for example. Any suitable electrically conductive silver or other type silk screen ink or paint such as is commercially available at present may be employed for this purpose such as, for example, that commercially known as Silpaint No. 1250-04 or Silpaint No. LO 1-1054, made by the Industrial Products Division of Handy & Harman of New York, New York. It should be understood, however, that the electrically conductive circuit leads 7a to 14a may be applied to the plastic base sheet 15 by various other methods such as, for example, by spraying, rolling or otherwise applying electrically con-ductive paint, paste or other conductive material to the plastic sheet 15, or by the use of well known vacuum metallization methods wherein aluminum or other vaporized electrically conductive material is vacuum deposited onto the plastic base sheet 15 through a masking screen or template. As shown in FIG. 1, the circuit leads 7a to 14a extend from the edge of the plastic base sheet 15 inwardly thereof to points which, on lamination of the two plastic sheets 15 and 16 together, underlie respective apertures 17 which are provided in the insulator sheet 16 for the purpose of enabling the electrical connection therethrough of each electrode section 7 to 14 to its respective circuit lead 7a to 14a. Although the circuit leads 7a to 14a are preferably terminated at one of the edges of the rectangularly shaped plastic base sheet 15, each as at one of its shorter edges as shown in FIGS. 1 to 3, they may be terminated instead at two or more of its edges, as desired.

Following the application of the circuit leads 7a to 14a to the plastic base sheet 15, a plurality of terminal contact members 7b to 14.5 for the respective circuit leads 7a to 14a are then temporarily fastened or tacked in place on the plastic base sheet 15 in positions overlying and in electrical contact with the outer end portions of the respective circuit leads 7a to 14a and projecting outwardly therefrom beyond the edge of the base sheet 15, as shown in FIG. 2. The terminal contact members 7b to 1412, which may suitably consist of copper strip or aluminum foil or ribbon, or preferably a wire cloth such as Phosphor-bronze cloth for example, may be temporarily tacked in place to the plastic base sheet 15 by suitably softening sinail underlying localized areas of the sheet, as by means of a soldering iron for instance, at points adjacent its outer marginal edge. The plastic base sheet 15 with the terminal contact members 7b to 14b thus temporarily fastened in place thereon, is then laminated under heat and pressure, at that side thereof provided with the circuit leads 7a to 14a, together with the plastic insulating sheet 16 to thereby form the base circuit component or assembly 18 (FIG. 2) of the composite electrode base assembly 6. The two sheets 15 and 16 are laminated together in proper registered position with each other with the apertures 17 in the insulator sheet 16 overlying the inner end extremities of the circuit leads '7a to 14a so as to expose the latter through the said apertures. During the lamination of the two sheets 15, 16 together, the terminal contact members 7b to 14b are embedded in and sealed between the two sheets so as to become firmly fastened thereto in good electrical contact with the respective circuit leads 7a to 14a. The laminating together of the two plastic sheets 15, 16 is preferably effected in a manner such as to cause those portions of the base sheet 15 and associated circuit leads 7a to 14a lying opposite the apertures 17 to be pressed and deformed into the apertures so as to lie ush with the exposed face of the insulator sheet 16 in the finished laminate or assembly 18. A continuous flat or smooth surface is thus provided on the insulator sheet side 16 of the assembly 18 on which to apply the segmented electrode 5. The exposure of the circuit leads 7a to 14a within the apertures 17 so as to lie flush with the electrodecarrying face of the assembly 18 assures the effective contacting of the exposed portions of the circuit leads by, and their good electrical connection to their respective electrode sections 7 to 14 on application of the latter to the assembly 1S. The lamination of the two plastic sheets 15, 16 to achieve the above mentioned result may be carried out, for example, in a suitable hydrostatic laminating press such as described and claimed in U.S. Patents 2,945,976, Fridrich et al., and 3,047,052, Fridrich, both assigned to the assignee of the present invention and employing a exible or conformable diaphragm for applying the laminating pressure to the thermoplastic base sheet 15 and pressing it, when softened by the laminating heat, into tne apertures 17 in the insulator sheet 16.

After the lamination of the plastic insulator sheet 16 to the plastic base sheet 15 to form the base circuit component or prelaminate 18, the segmented back electrode layer 5 comprised of the individual electrode sections 7 to 14 is then applied onto the surface of the plastic insulator sheet 15 of the prelaminate 18 to thereby complete the fabrication of the composite electrode base assembly 6, as shown in FIGS. 3 and 4. The discrete electrode sections 7 to 14 may be applied in the desired pattern on the plastic insulator sheet 16 of the prelaminate 1S by any suitable coating or deposition process, as by a silk screen printing process employing an electrically conductive silk screen ink or paint for the electrode sections. Any suitable conducting silver or other type silk screen ink or paint such as is commercially available at present may be employed for this purpose such as, for example, that known as Silpaint No. LO 5-1162 or LO 6-1150 made by the Industrial Products Division of Handy & Harman of New York, New York, or Silver Composition No. 7095 of the Group 4 series of conductive liquid silver preparations made by the Electrochemicals Department of the E. I. du Pont de Nemours & Company of Wilmington, Delaware. Alternatively, the back electrode sections 7 to 14 may be comprised of some form of electrically conductive paint, paste, or similar conductive material which may be sprayed, rolled, or otherwise applied onto the insulating layer 3 as through a masking screen or template so as to form the array of discrete electrode sections. Thus, the same electrically conductive lacquer material as is employed for the front electrode layer 4 may also be used for the back electrode sections 7 to 14. As another alternative, the electrode sections 7 to 14 may be formed by well known vacuum metallization methods wherein aluminum or other vaporizable electrically conductive material such as, for example, tin oxide, is vacuum deposited onto the plastic insulator sheet 16 of the prelaminate 18. During the application of the electrode coating material to the plastic insulator sheet 16 to form the segmented electrode thereon, the coating material forming each electrode sections 7 to 14 contacts the respective circuit leads '7a to 14a exposed within the apertures 17 so as to electrically connect therewith, as clearly shown in FIG. 4. Although the thickness of the electrode sections 7 to 14 is not critical, they are preferably made as thin as possible while still possessing adequate electrical conductivity as determined, in general, by a resistance no greater than around 1000 ohms per square or so. Thus, the thickness of the electrode sections 7 to 14 will vary according to the electrical conductivity of the material employed therefor. In the case of the conventional commercial type silver silk screen inks or paint compositions such as referred to above, however, it has been found that the electrical conductivity of electrode sections 7 to 14 around 10 to 30 microns or so in thickness are entirely adequate for the purposes of the invention.

The electrode base assembly 6 formed as described above may then be provided, on the side thereof carrying the segmented electrode 5, with the previously mentioned insulating layer 3, phosphor-bearing layer 2, and light-transmitting front electrode layer 4 to form an electrically active assembly 19 as shown in FIG. 5, which itself may be utilized as an electroluminescent display device. In such case, it is provided with a terminal contact member 4b similar to the other terminal Contact members 7b to 14b and suitably connected electrically to the front electrode layer 4, as by means of an electrically conductive cement, for instance. The insulating layer 3, phosphor layer 2, and front electrode layer 4 may be applied to the electrode base assembly 6 in any suitable manner. Thus, where the front electrode layer 4 is comprised of an electrically conductive lacquer as referred to hereinabove, the three layers 3, 2 and 4 may be successively coated in the form of suspensions directly onto the electrode base assembly 6 as by means of a conventional doctor blade coating device, with each layer being dried before application of the next layer thereover. Preferably, however, they are preliminarily coated in the form of suspensions onto a temporary support or release sheet of a thin, flexible film material such as polyethylene terephthalate or polytetrauoroethylene, which are commonly known as Mylar and Teflon, respectively, from which they are then removed or peeled off as an integrated multilayer film 20, as shown in FIG. 6, and sheets of the proper size then cut therefrom and laminated under pressure and heat to the electrode base assembly 6. As shown in FIG. 7, and particularly in the case where the front electrode layer 4 is comprised of electrically conductive glass paper as referred to hereinabove, the front electrode layer 4, instead of being formed as a coating on the phosphor layer 2, or being laminated thereto, may be coated on or prelaminated to a thin, flexible sheet 21 of a suitable transparent organic thermoplastic material, preferably one having hydrophilic properties such as that referred to above as suitable for use for the plastic base sheet of the composite back electrode base assembly 6. The coated sheet or prelaminate 22 thus formed, or alternatively just a sheet of electrically conductive glass paper by itself, may then be laminated under pressure-and heat together with either a composite electrode base assembly 6 coated with the insulating and phosphor layers 3 and 2, or together with a composite electrode base assembly 6 and a separate multilayer lm 23 composed of the insulating and phosphor layers 3 and 2, as shown in FIG. 7. During this laminating operation, the terminal contact member 4b for the front electrode layer 4 becomes firmly embedded in place within the laminate, in

8 pressure contact with the front electrode layer 4 so as to form a good electrical connection therewith.

Because the light output of an electroluminescent cell deteriorates rapidly on exposure to water vapor, such as the moisture normally present in the atmosphere, it is preferable to encapsulate the electrically active elements of the electroluminescent display device 1 according to the invention in a substantially vapor-tight enclosure as well as to also incorporate suitable water-vapor barrier layers therein. Accordingly, as shown in FIGS. 6 and 7, the electrically active elements 2, 3 and 4 and the composite electrode base assembly 6 of the electroluminescent display device 1 according to the invention are preferably laminated between outer encapsulating sheets 24 and 25 of licht-transmitting thermoplastic material of low water vapor permeability which overreach the margins of the elements 2, 3, 4, 5 and 6 and are sealed together around their marginal edges, with the contact terminal members 4b and '7b to 14h embedded in the marginal seal and projecting outwardly therebeyond. The outer encapsulating sheets 24 and 25 are made of a light-transmitting organic thermoplastic material of tough and stable character and high impermeability to moisture and preferably flexible in nature. Among the materials which may be satisfactorily employed for this purpose are polyethylene, polytetrailuoroethylene, polychlorotrilluoroethylene, polystyrene, methyl methacrylate, polyvinylidine chloride, polyvinyl chloride, polycarbonate materials such as, for example, the reaction products of diphenyl carbonate and Bisphenol A, and polyethylene terephthalate. The material preferably employed for such purpose, however, consists of polychlorotrifluoroethylene lm, cornmonly known as Kel-F, of approximately 0.005 inch thickness.

To produce such an encapsulated electrolurninescent display device 1 according to the invention, an electrically active assembly 19 such as shown in FIG. 5 and comprised of the composite electrode base assembly 6 having the insulating, phosphor and front electrodes layers 3, 2 and 4 directly coated thereonto, may be laminated between the outer thermoplastic encapsulating sheets 24 and 25, preferably with an intervening transparent thermoplastic water-vapor barrier layer 21 such as described hereinabove disposed between the front electrode layer 4 and the front encapsulating sheet 25. Preferably, however, the composite electrode base assembly 6 according to the invention is simply stacked together with the other component elements of the electroluminescent display device between the two plastic outer encapsulating sheets 24 and 25, as in the manner shown in FIGS. 6 and 7 for example, to form a lay-up assembly 26 or 27 which is then laminated together under heat and pressure, preferably in an evacuated chamber, to form the completed electroluminescent display device 1 according to the invention. In the case of the lay-up assembly 26 shown in FIG. 6, the insulating layer 3, phosphor layer 2, and electrically conductive front electrode layer 4 are in the form of the preformed multilayer film 20 as described previously, which is placed in proper position on top the segmented electrode-carrying side of the composite electrode base assembly 6, and the terminal contact member 4b then positioned in contact with the electrically conductive front electrode layer 4 of the multilayer film 20 and temporarily heat-tacked in place to the bottom thermoplastic encapsulating sheet 24. The light-transmitting thermoplastic front watervapor barrier sheet 2li is next positioned on top the front electrode layer 4 of the preformed multilayer lm 20 and the front thermoplastic encapsulating sheet 25 then placed thereover. In the case of the lay-up assembly 27 shown in FIG. 7, a preformed multilayer film 23 as described previously in connection with FIG. 5 and comprised of the phosphor layer 2 and the insulating layer 3 is placed in proper position on top the segmented electrode-carrying side of the composite electrode base assembly 6, and the terminal contact member 4b then positioned in place thereover and temporarily heat-tacked in place to the bottom thermoplastic encapsulating sheet 24, as described previously. A multilayer sheet 22 cornposed of a thermoplastic water-vapor barrier sheet 21 faced with a front electrode layer 4 comprised of either a coating of a light-transmitting electrically conductive lacquer, or a sheet of electrically conductive glass paper laminated to the barrier sheet 21, as described hereinabove in connection with FIG. 5, is then placed over the multilayer film 23 with its conductive electrode side 4 next to the phosphor layer 2, following which the front thermoplastic encapsulating sheet 25 is then placed in proper position over the stacked assembly. Where the front electrode layer 4 is comprised of electrically conductive glass paper, it may be incorporated into the lay-up assembly 27 as a separate element, instead of being prelaminated to the thermoplastic water-vapor barrier sheet 21 to form a prelaminate therewith as shown in FIG. 7. In such case, the terminal Contact member 4b may then be positioned on top the electrically conductive glass paper electrode 4, instead of below it as shown in FIG. 7.

The laminating of the lay-up assembly 26 or 27 may be carried out in any suitable laminating press which will subject the assembly to laminating heat and pressure, while under a vacuum for removing undesired gaseous materials therefrom. For such purpose, the lamination of the lay-up -assembly 26 or 27 may be advantageously performed in the manner, and by the use of a hydrostatic laminating press such as described and claimed in the aforementioned Fridrich et al. Patent 2,945,976 or in Fridrich Patent 3,047,052. The stacked lay-up assembly 26 or 27 is placed between the top and bottom press platens of the hydrostatic press, beneath a conformable diaphragm positioned between the press platens, the conformable diaphragm being constituted of a tiexible gasimpervious sheet material Stich as soft-annealed aluminum foil or polyethylene terephthalate film such as Mylar. Compressed air or other fiuid is admitted into the closed chamber of the press over the diaphragm therein to exert hydrost-atic pressure on the stacked lay-up assembly, vacuum is supplied under the diaphragm to remove any trapped gases or moisture from the space therebelow and from the lay-up assembly in the said space, and heat is then applied by suitable means to the stacked assembly, as by passing an electric current through the metal foil diaphragm, in order to cause the plastic encapsulating sheets 24 and 25 to soften and seal together at their margins so as to encapsulate the lay-up assembly. During the laminating process, the terminal contact members 4b and 7b to 14b become embedded in the marginal seal between the plastic sheets 24, 25. At the same time, the terminal contact member db is pressed into intimate contact with the front electrode layer 4 so as to make good electrical contact therewith.

The modified form of, and method of constructing an electroluminescent display device 1 according to the invention as disclosed in FIGS. 8-11 differ from the previous form of the invention principally in the manner of connection of the light-transmitting front electrode layer 4; to its terminal contact member 4b, and in the provision of a completely water-va-por impermeable additional back barrier layer on the non-light-transmitting side of the display device. For this purpose, -a thin layer 28 of metal foil, such as aluminum foil for example, is laminated to the underside of the base circuit component or prelaminate 18 to form a modified base circuit component 18 as shown in FIG. 8, one end of the metal foil 2S being folded around the end of the base circuit prelaminate opposite its terminal contact end to form an upper contact strip portion 29 which is laminated to the plastic sheet 16 of the prelaminate 18'. Because of its complete impermeability to water vapor, the metal foil backing sheet 2S thus affords complete protection against the ingress of moisture into the display device 1 through the back side thereof. The lamination of the metal foil backing sheet 28 to the base circuit prelaminate 18 may be effected separately from, i.e., subsequent to, the lamination together of the plastic sheets 15 and 16 to form the base circuit component or prelaminate. Preferably, however, it is laminated to the base circuit component or prelaminate 18' simultaneously with the lamination together of the plastic sheets 15 and 16 to form the base circuit component. During the lamination of the metal foil backing sheet 2S to the plastic base sheet 15, a terminal contact member 4b as described previously is also laminated to the metal foil sheet 28, preferably in a position between the latter and the adjacent plastic base sheet 15 and projecting outwardly therefrom alongside and in a row with the other contact terminal members 7b to 14]), as shown. The resulting metal foil-faced base circuit component 18 thus formed (FIG. 8) is then provided on its upper or plastic insulator sheet side 16 with a segmented back electrode layer 5, such as described hereinbefore in connection with FIGS. 1-7 for example, to thereby form a modified type of composite electrode base assembly 6 (FIG. 9).

To complete the Ifabrication of an electroluminescent display `device 1 employing such a modified form of electrode base assembly 6', any of the various procedures described hereinabove in connection with FIGS. 1 to 7 may be followed, the only differences being that the phosphor and insulating layers 2 and 3 are terminated short of the bent-over contact strip 29 of the assembly 6 so as to leave it exposed Ias shown in FIG. 11, and that the front electrode layer 4 overreaches the said bent-over contact strip 29 so as to electrically contact therewith. The preferred manner, however, of fabricating such a m-odified form of electroluminescent display device is by laminating together a lay-up assembly 30 such as shown in FIG. 11 and comprised of the modified electrode base assembly 6 over the electrode-carrying side -of which is placed a preformed double-layered film 23 consisting of the phosphor and insulating layers 2 and 3 and terminating short of the bent-over contact strip 29 of the assembly 6 so as to leave it exposed. As shown, the insulating layer side 3 of the double-layered film 23 is placed next to the segmented electrode side 5 of the electrode base assembly 6. Placed over the phosphor layer 2 of the film 23 is a preformed front electrode subassembly 22 similar to the subassembly 22 previously described in connection with FIG. 7 and comprised of a front electrode layer 4 consisting either of an electrically conductive lacquer coated onto, or an electrically conductive glass paper prelaminated to, a transparent thermoplastic water-vapor barrier sheet 21. As shown, the electrode side 4 of the subassembly 22' is placed next to the phosphor layer 2, and it extends beyond the phosphor-insulating film 23 so as to overlie and electrically contact the bent-over contact strip 29 of the assembly 6 during the lamination together of the lay-up assembly 3f?.

As shown more particularly in FIG. 10, the front electrode subassembly 22 preferably is additionally provided along that edge of its plastic sheet component 21 which overlies the contact strip 29, and particularly in the case of display devices lof large surface area along the two adjacent edges of the plastic sheet 21 as well, with a thin continuous stripe 31 of electrically conductive material, eg., a silver paint such as employed for the circuit leads 7a to 14a, which is applied to the same side of the plastic sheet 21 as the front electrode layer 4 and is overlapped by the front electrode layer so as to electrically connect therewith. On lamination of the lay-up assembly 30, the portion of the conductive stripe 31 overlying the bent-over contact strip 29 contacts and thus becomes electrically connected to the contact strip 29. The conductive stripe 31 thus operates conjointly with the bent-over contact strip 29 to electrically connect the front electrode layer 4 to the metal foil backing sheet 2S. A better electrical connection between these elements is thereby afforded such as is of added advantage, particularly in the case of display devices 1 of large surface .area since it acts to distribute the applied electrical potential over a greater portion of the surface area of the front electrode layer 4, thereby insuring against overheating of the front electrode layer by the applied current load. Another advantage of such an improved electrical connection is that it permits operation of display devices 1, of the type employing front electrodes 4 of electrically conductive lacquer, at higher voltages and 'frequencies without overloading and overheating of the conductive lacquer such as would cause disintegration and electrical breakdown of the plastic matrix material thereof with resultant loss of electrical contact to the front electrode.

The lay-up of the electrode base assembly 6', the combined phosphor-insulating lilm 23, and the front electrode assembly 22 is stacked between the outer thermoplastic encapsulating sheets 24 and 25 to complete the lay-up assembly shown in FIG. ll, which assembly is then laminated together under heat and pressure, while subjected to a vacuum, in a suitable laminating press to thereby complete the fabrication of the electrolurninescent display device 1. The lamination of the lay-up assembly 30 may be carried out, for example, in the same manner, and by the use of the same hydrostatic laminating press as described hereinabove in connection with FIGS. 6 and 7.

For certain applications, as 'for instance Where it is desired to adapt the display device 1 for sliding insertion of its terminal contacts 4b and 7b to 1419 into a lamp holder socket, the display device may be provided with suitable stitfening means such as shown in FIGS. 12 and 13 yand disclosed and claimed in copending U.S. application Serial No. 149,653, Devol et al., led November 2, 1961, and assigned to the same assignee as the present invention. As therein disclosed, and as shown in FIGS. 12 and 13, such a stilfening means suitably comprises a layer 32 of open-weave cloth material, for instance, a cotton cloth material such as muslin cloth, preferably bleached muslin cloth, overlying and laminated to the outer side of the plastic encapsulating sheet 24 of the display device so as to be partially embedded in the plastic sheet 24 and thus interlocked therewith yagainst relative displacement, and a stiffening overlay 33 of a relatively sti thermoplastic sheet material in which the cloth layer 32 is also partially embedded so as to be likewise interlocked therewith against relative displacement. The stiff plastic sheet overlay 33 may be composed of any thermoplastic material having a softening or heat distortion temperature appreciably below, for example, at least C. or so below, the laminating temperature of the lay-up assembly 30 so that the lamination of the plastic sheet overlay 33 to the previously laminated assembly 30 can be eifected at a temperature which will not result in softening of any of the component layers of the laminated yassembly 30 with consequent liklihood of damage thereto. Examples of thermoplastic materials suitable for the plastic stiffening sheet or overlay 33 are cellulose acetate, cellulose acetate butyrate, polyethylene, acrylic resins, polystyrene and polycarbonate resins such as, for example, that commercially known as Lexan made by applicants assignee, General Electric Company. The thermoplastic stiifening sheet or overlay 33 should be of sufficient thickness to impart the desired degree of stiffness to the lnished electroluminescent display device 1. Thus, where polystyrene such as that commercially referred to as Hi-Impact polystyrene is employed for the plastic stiiening sheet 33, a sheet thickness around 30 mils or thereabouts will impart ample stillness to the finished electroluminescent display device.

As shown in FIG. 13, the laminated cloth layer 32 and plastic stiiener sheet or overlay 33 preferably extend beyond the marginal edge of the device from which the terminal contact members 4b and 7b to 14h extend, in order to provide a projecting stift support ilange or electrical connection board 34 to which the terminal contact members 4b and 7b to 14h are laminated so as to lie approximately flush therewith. The rigid electrical connection or terminal board 34, with its Hush-mounted terminal contact members 4b and '7b to 14h, affords a convenient means for mounting the display device 1 in, and electrically connecting its terminal members to the contacts of an electrical socket for the device, such as a conventional gang-type socket having its contacts arranged in a row and concealed within a slot-shaped opening in the socket housing. The display device 1 is insertable into such a socket by a simple push-in insertion of the terminal board portion 34 of the device into the slot-shaped opening of the socket so as to engage with the contacts therein.

ln the operation of the electroluminescent display device 1 according to the invention, a source of alternating current potential is connected between the contact terminal 4b and any preselected one or more of the contact terminals 7b to 14h. The A.C. potentials thus applied to the appropriate electrode sec-tion or sections 7 to 14 of the segmented electrode 5 causes the selected electrode section or sections to excite to luminescence the portions of the electroluininescent phosphor located between the said electrode section(s) and the front electrode 4. A corresponding luminous pattern, conforming to that of the energized back electrode section(s), is thus produced and emitted by the display device l. By providing a suitable switching arrangement between the A.C. source and each of the contact terminals 7b to 14b, a selected luminous pattern, which in the case of the particular digital display device 1 illustrated may be in the form of any digit from 0 to 9, can thus be made to appear at the light-emitting or viewing side of the display device, either as a lighted configuration against a darkened background, or as a darkened configuration against a lighted background. For example, where it is desired to display the digit l as a lighted conliguration against a darkened background, an electrical potential is applied across the front electrode 4 and the sections 7, 8 (or 10, 11) of the back electrode 5. Conversely, where it is desired to display the digit 'l as a darkened coniiguration against a lighted background, the electrical potential is then applied instead across the front electrode 4 and all the back electrode sections 9 to 14 other than the two electrode sections 7, S (or 11, 12) which are to remain unenergized to thus form the darkened digit 1. During the operation of the display device, the plastic insulator sheet 16 of low permittivity which, in accordance with the invention, is provided between the leads 7a to 14a and the segmented electrode layer 5 to electrically insulate them from one another other than at their points of connection, effectively prevents the leads 7a to 14a from capacitively coupling to the light-transmitting front electrode layer 4 and so exciting to luminescence the overlying portions of the electroluminescent phosphor layer 2 to the detriment of the appearance of the luminous pattern produced by the display device.

By providing, in accordance with the invention, the plastic insulator sheet 16 of low dielectric constant or permittivity as an insulating separator between the electrode leads 7a to 14a and the various electrode sections 7 to 14 (other than at the points of electrical connection of each lead to its respective electrode section), it is possible for the lead to any individual electrode section to extend therefrom to the edge of the display device in a path extending across, but without the lead electrically contacting any of the other electrode sections. As a result, there is no need for spacing any of the electrode sections 7 to 13, delineating the ligure 8, suciently far apart from one another to permit passage therebetween of a lead without touching and electrically contacting such electrodes. Consequently, the discrete electrode sections 7 to 13 of the display device 1 according to the invention need only be spaced apart a very slight distance of as little as .001 inch or so, just suliicient to insure their not electrically contacting one another, at the points or regions where they meet. Because of this, the electroluminescent display device construction according to the invention permits maximum utilization of the available surface area thereof for display purposes, with resulting greatly improved definition or delineation of the illuminated display pattern produced by the device such as, for example, the digits to 9 in the case of the particular digital display device 1 described and illustrated herein. Moreover, the use in accordance with the invention of a preformed apertured insulator sheet 16 of low permittivity plastic material for the purpose of electrically insulating and shielding the back electrode current supply leads 7n to 14a from all the electrically active components of the dispay device other than the respective electrode sections 7 to 14 to which each particular lead is connected, serves to greatly simplify and facilitate the construction and manufacture of an electroluminescent display device of the edge contact terminated type which is not subject to excitation of, and resulting undesired light emission lfrom those portions of the phosphor layer directly overlying the current supply leads to the segmented back electrode by reason of the applied A.C. potential.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electroluminescent display device comprising a segmented back electrode assembly comprised of a thermoplastic base sheet provided on one side with a plurality of circuit leads consisting of coatings of electrically conductive material and an apertured insulator sheet of low dielectric constant organic thermoplastic material adhered at one side to said base sheet over the said circuit leads thereon and having a plurality of discrete electrode sections on its other side comprised of coatings of electrically conductive material forming a segmented back electrode, said insulator sheet having a plurality of apertures therein registered with respective ones of and through which the said electrode sections and cir-cuit leads are electrically interconnected, an electroluminescent phosphor layer overlying the said insulator sheet and the segmented back electrode thereon, and a light-transmitting front electrode layer overlying said phosphor layer, said circuit leads extending to the edge of the said base sheet and being insulated by said insulator sheet from capacitively coupling to the said front electrode upon application of an A.C. potential to the said leads and front electrode.

2. An electroluminescent display device as specified in claim 1 having, in addition, an insulating layer of high dielectric constant material disposed between the said phosphor layer and the said segmented back electrode.

3. An electroluminescent display device as specified in claim 2 having, in addition, a front water-vapor barrier layer of a light-transmitting hydrophilic thermoplastic material overlying the said front electrode layer, an outer encapsulating envelope comprised of sheets of lighttransmitting thermoplastic material of low water-vapor permeability adhered `to the opposite sides of the display device and sealed together around their periphery, and a plurality of terminal contact members sealed through the peripheral seal between the said thermoplastic encapsulating sheets and electrically connected respectively to the said front electrode layer and to respective ones of said circuit leads. d

4. An electroluminescent display device comprising a segmented back electrode assembly comprised of a thermoplastic base sheet provided on one side with a plurality of circuit leads consisting of coatings of electrically conductive material and an apertured insulator sheet of low dielectric constant organic thermoplastic material adhered at one side to said base sheet over the said circuit leads thereon and having a plurality of discrete electrode sections on its other side comprised of coatings of electrically conductive material forming a segmented back electrode, said insulator sheet having a plurality of apertures therein registered with respective ones of and through which the said electrode sections and circuit leads are electrically interconnected, a sheet of metal foil adhered to the side of said thermoplastic base sheet opposite the side thereof provided with the said circuit leads and having a contact strip portion extending around and overlying a narrow marginal edge portion of the insulator sheet, an electroluminescent phosphor layer overlying the said insulator sheet and the segmented back electrode thereon but spaced edgewise from the said contact strip portion of said metal foil sheet, a light-transmitting front electrode layer overlying said phosphor layer and said contact strip portion and in electrical contact therewith, and a plurality of terminal contact members electrically connected respectively to the said metal foil sheet and to respective ones of said circuit leads.

5. An electroluminescent display device as specilied in claim 4 wherein the said terminal contact members project from the edge of the device opposite that edge thereof provided with the said contact strip portion, and wherein a front water-vapor barrier layer overlies the said front electrode layer and is provided with a narrow stripeshaped coating of electrically conductive material overlying and in electrical contact with the said contact strip portion of the metal foil sheet and overlapped by said front electrode layer so as to be electrically connected thereto.

6. An electroluminescent display device as specied in claim 5 wherein the said stripe-shaped conductive coating along the edge of the front barrier layer overlying the contact strip portion of the metal foil sheet is extended along both adjacent marginal edges of the front barrier layer to provide conductor extensions which are also overlapped by the said front electrode layer so as to be electrically connected thereto.

7. An electrode subassembly for an electroluminescent display device comprising a thermoplastic base sheet provided on one side with a plurality of circuit leads consisting of coatings of electrically conductive material, an apertured insulator sheet of low dielectric constant organic thermoplastic material adhered to said base sheet over the said circuit leads thereon and having a plurality of apertures therein registered with respective ones of said circuit leads, the portions of said base sheet and associated circuit leads opposite the said apertures being displaced thereinto so as to lie flush with the outer side of said insulator sheet, and a plurality of discrete electrode section-s comprised of coatings of electrically conductive material on the outer side of said insulator sheet and overlying respective yones of said apertures and the portions of the circuit leads displaced thereinto so as to contact and electrically connect therewith.

8. An electrode subassembly as specified in claim 7 having, in addition, a plurality of terminal contact members embedded between and projecting outwardly beyond the marginal edges of the said thermoplastic sheets and in electrical contact with respective ones of said circuit leads.

9. An electrode subassembly as specified in claim 7 having, in addition, a sheet of metal foil adhered to the outer side of said base sheet and extending around an edge of the interadhered base and insulator sheets to form a narrow band portion overlying the marginal edge of the outer side of said insulator sheet and adhered thereto.

References Cited by the Examiner UNITED STATES PATENTS 3,008,065 1l/l961 Chamberlin 313-108 GEORGE N. WESTBY, Primary Examiner.

JEROME SCHNALL, Examiner. 

1. AN ELECTROLUMINESCENT DISPLAY DEVICE COMPRISING A SEGMENTED BACK ELECTODE ASSEMBLY COMPRISED OF A THERMOPLASTIC BASE SHEET PROVIDED ON ONE SIDE WITH A PLURALITY OF CIRCUIT LEADS CONSISTING OF COATINGS OF ELECTRICALLY CONDUCTIVE MATERIAL AND AN APERTURED INSULATOR SHEET OF LOW DIELECTRIC CONSTANT ORGANIC THERMOPLASTIC MATERIAL ADHERED AT ONE SIDE TO SAID BAASE SHEET OVER THE SAID CURCUIT LEADS THEREON AND HAVING A PLURALITY OF DISCRETE ELECTRODE SECTIONS ON ITS OTHER SIDE COMPRISED OF COATINGS OF ELECTRICALLY CONDUCTIVE MATERIAL FORMING A SEGMENTED BACK ELECTRODE, SADI INSULATOR SHEET HAVING A PLURALITY OF APERTURES THEREIN REGISTERED WITH RESPECTIVE ONES OF AND THROUGH WHICH THE SAID ELECTODE SECTIONS AND CIRCUIT LEADS ARE ELECTRICALLY INTERCONNECTED, AN ELECTROLUMINESCENT PHOSPHOR LAYER OVERLYING THE SAID INSULATOR SHEET AND THE SEGMENTED BACK ELECTRODE THEREON, AND A LIGHT-TRANSMITTING FRONT ELECTODE LAYER OVERLYING SAID PHOSPHOR LAYER, SAID CURCUTI LEADS ECTENDING TO THE EDGE OF THE SAID BASE SHEET AND BEING INSULDATED BY SAID INSULATOR SHEET FROM CAPACITIVELY COUPLING TO THE SAID FRONT ELECTRODE UPON APPLICATON OF AN A.C. POTENTIAL TO THE SAID LEADS AND FRON ELECTRODE. 